This research will focus on chemical characterization and the mechanism of action of heat-stable enterotoxins (ST) produced by porcine, bovine, and human strains of enterotoxigenic (ENT) Escherichia coli. Characterization will include molecular weight determination, chemical analysis, amino acid analysis, identification of end-groups, and the primary amino acid sequence. The mechanism of action of ST will be studied using the rat perfusion model to measure fluid and electrolyte fluxes and possible enzyme-mediated absorptive responses. Ion fluxes in isolated porcine intestinal epithelium will be observed. Also, the binding of radioactive ST to intestinal cells in isolated and to purified intestinal membranes will be studied. The nature of the receptor site(s) for ST will be characterized and identified. Additional work will look at the immunogenic properties of ST conjugated to bovine serum albumin and development of a rapid diagnostic test. The subunit structure of purified heat-labile enterotoxin (LT) produced by ENT plus E. coli will be characterized and the mechanism of action studied using whole cells and lysates of pigeon erythrocytes. The interaction of purified LT from porcine and human strains with small intestinal cells in isolated loops, purified intestinal membranes and pigeon erythrocyte membranes will be studied. Binding phenomena and the receptor(s) for LT will be characterized. Experiments on the mechanism of action of LT will look at the role of purified subunits or degradation of LT by membranes to produce fragments with enzymatic activity.